Although he has been in the limelight for a decade, the official career of the 22-year-old pianist Benjamin Grosvenor began only when he graduated from the Royal Academy of Music two ­summers ago. He celebrated by opening the BBC Proms that year and has been a frequent, popular guest ever since. On Monday ­1 September he gives a lunchtime recital at London’s Cadogan Hall, home of Proms chamber concerts. The broadcaster boasts its 2004 discovery of him in the final of the Young Musician of the Year competition, though the judges actually gave the award to Nicola Benedetti, who was five years older, gambling perhaps that the 11-year-old would return. Decca got in first, however, and made him an exclusive artist, its first British pianist for 60 years. His third album, Dances,